This research proposal is concerned with the auditory, phonetic and lexical processes that constitute the early perceptual analysis of a speech signal. Experimental procedures involving selective adaptation, reaction time, discrimination and dichotic monitoring will be used in conjunction with synthetic speech, complex nonspeech and natural speech stimuli. These studies will test current speech perception theories and aid in outlining the processes and capacity limitations involved in the auditory to phonetic to lexical coding of speech. Experiments will examine the role of auditory processing in speech perception. Some experiments are designed to investigate which aspects of phonetic distinctions are mediated by auditory coding processes. Others will examine whether auditory features are extracted separately and independently of each other for later combination or whether feature extraction operates in a wholistic fashion. Experiments on the combined effects of auditory and phonetic processes will further investigate the role of feature detectors in both auditory and phonetic processes, the role of contextual information in speech processing and the contribution and nature of uniquely phonetic processes in speech recognition. Experiments using a dichotic monitoring procedure will investigate capacity limitations and automaticity in phonetic processing. These experiments will outline the processing and resource allocation involved as information from higher level (lexical) processes meets information from lower level (auditory to phonetic) processes. The results of these studies will be used to refine and elaborate an information processing model of speech perception that has been implemented as a computer simulation. This model can serve as a normative base against which theories of developmental processes or disorders can be compared.